Comparison of Saccharomyces cerevisiae strains in co-fermentation with Pichia kluyveri

Abstract

A strain of Pichia kluyveri has been commercialised recently for use in co-fermenting white wines with Saccharomyces cerevisiae. The strain provides improved mouth feel and aroma characters, but requires good growth and fermentation by S. cerevisiae to complete the ferment. This research was conducted to assess the level of variation between S. cerevisiae strains in their capability for growth and co-fermentation with this strain of Pichia. An initial screening experiment conducted to find variation between strains measured fermentation rate and viable cell titre. None of the 11 commercial strains, tested in the screen were negatively impacted by cofermentation with Pichia suggesting that the new commercial Pichia strain should be compatible with most commercial isolates of S. cerevisiae. However, there were clear indications of strain differences. More detailed profiling of seven strains revealed three different co-fermentation profiles, each represented by a S. cerevisiae strain: 1. S. cerevisiae strain F15 inhibited Pichia growth 2. Pichia inhibited S. cerevisiae strain S288c growth and fermentation 3. S. cerevisiae strain M2 was neutral in co-ferments with Pichia Varying fermentation conditions were tested to identify the conditions which best show the variation in co-fermentation. Higher temperatures helped Saccharomyces gain a competitive advantage over Pichia but the addition of nitrogen as either DAP or proline had no significant effect on the co-fermentation profiles. F2 recombinants between F15 and M2 were phenotyped and scored for their ability to inhibit Pichia during fermentation. The results show the trait to be inherited, and suggest the phenotype may be linked to two genetic loci. F2 recombinants between BY4761 (an S288c derivative) and RM11-1a (which shows neutral behaviour similar to M2) showed non-Mendelian inheritance, with all F2’s tested showing phenotypes similar to S288c. New F1 hybrids between S288c and RM11-1a did not show the phenotype of inhibition by Pichia; however F2 recombinants sporulated from these showed the S288c-like phenotype, confirming the hypothesis that the phenotype is linked to a non- Mendelian element.